[illumos-Developer] Proposal: Add memory clearing allocator to libnvpair

[Jason King]

Something that's hopefully minor and not controversial.  I was
planning to do this for the work I'm doing with the IKEv2 support, but
figured it's probably generally enough useful to live outside of it.

The libnvpair library (userland) normally uses the malloc/free
commands for its memory requirements.  It also specifies a pluggable
allocator interface for use with the nvlist_xalloc(3nvpair) and
nvlist_xdup(3nvpair) function.  I would like to propose to add to
libnvpair an allocator that zeros out the memory when allocated and
freed.  This would be useful in situations where nvlists may contain
sensitive information such as passwords/pins/keys/etc.

Specifically, add to libnvpair.h

extern nv_alloc_t *nv_alloc_zero;

Programs can then use (return codes elided for clarity):

nvlist_t *nvl;
int flags = ...; /* NV_UNIQUE_NAME, NV_UNIQUE_NAME_TYPE or 0 */

nvlist_xalloc(&nvl, flags, nv_alloc_zero);
...
add/remove data from nvlist
...
nvlist_free(nvl);

And the memory used will be zeroed out before being returned to the
system via free(3c).